 This study found that the amount of time spent playing football and the severity of the impacts experienced during play were both linked to the presence of chronic traumatic encephalopathy, CTE. The researchers used a position exposure matrix, PEM, to measure the amount of time each player was exposed to certain types of impacts while playing football. They then compared these measurements to the presence of CTE in the brains of deceased football players. The results showed that the longer a person played football and the more severe the impacts they experienced, the higher their risk of developing CTE. This suggests that repeated blows to the head may be responsible for the development of CTE. This article was authored by Daniel H. Dineshvar, Evan S. Ney, Zachary H. Borkam, and others.